The present invention relates to a filtration cartridge using hollow fiber membranes which is set in a tank type filtration apparatus or a rack type filtration apparatus. More particularly, the present invention relates to a hollow fiber membrane cartridge used in a filtration apparatus for removing turbidity and bacteria from a large volume of raw water such as river water, lake water, underground water, sea water, life waste water or industrial waste water.
The present invention relates also to a tank type or rack type filtration apparatus using the above-mentioned hollow fiber membrane cartridge(s).
JP-A-61-153104 discloses, as a conventional cartridge using hollow fiber membranes, the cartridge shown in FIG. 3 which has the following structure: a plurality of hollow fiber membranes are accommodated in a cylindrical casing, both ends of each hollow fiber membrane are fixed to the cylindrical casing in upper and lower, respectively, adhesion and fixation portions, and the cylindrical casing is a casing integrally molded so as to extend to the upper and lower ends of the hollow fiber membranes. The hollow portions of a large number of the hollow fiber membranes are open in the upper adhesion and fixation portion of the cartridge but are sealed in the lower adhesion and fixation portion, and an adhesive layer in the lower adhesion and fixation portion has a plurality of through-holes. An air chamber surrounded by the cylindrical casing is formed under the lower adhesion and fixation portion.
This hollow fiber membrane cartridge is for filtration under external pressure and is used after being set in a filtration column. When materials incapable of permeating the membranes are accumulated on the outer surfaces of the membranes, the filtering capability of the membranes is deteriorated, and therefore a washing procedure for removing the accumulated materials on the surfaces of the membranes is carried out after filtration for a definite time.
A method for washing called air bubbling is known. This method comprises the steps of introducing air into the hollow fiber membrane cartridge through its lower portion in a filtration column filled with raw water, and vibrating the hollow fiber membranes in a gas-liquid mixed fluid to peel off the accumulated materials on the surfaces of the membranes.
However, in the hollow fiber membrane cartridge, air bubbling does not permit sufficient washing in some cases because both ends of each hollow fiber membrane are fixed to the cylindrical casing, so that the vibration of the hollow fiber membranes is limited. This phenomenon is remarkable and causes troubles in some cases in a long-term filtration operation, particularly when the outside diameter of the cartridge is large.
In order to solve such problems, the present invention is intended to provide a hollow fiber membrane cartridge which facilitates the peeling-off of suspended materials accumulated on the outer surfaces of hollow fiber membranes by enabling each hollow fiber membrane to vibrate as much as possible at the time of washing by air bubbling, and permits easy discharge of the peeled-off suspended materials from the hollow fiber membrane cartridge.
That is, the present invention relates to a hollow fiber membrane cartridge comprising a bundle of a plurality of hollow fiber membranes, both ends of which are fixed by adhesion, a cartridge head fixed at the periphery of the bundle at one end so as not to permit the passage of liquid either in or out, and a bottom ring fixed at the periphery of the bundle at the other end so as not to permit the passage of liquid either in or out, wherein the cartridge head and the bottom ring are not connected or fixed but are separated. The hollow portion at the end of each hollow fiber membrane on the cartridge head side is open, the hollow portion at the end of each hollow fiber membrane on the bottom ring side is sealed, and a plurality of through-holes are provided in an adhesion and fixation layer on the bottom ring side. In one embodiment of the present invention, the end of the bottom ring is fixed by adhesion to the periphery of the bundle of the hollow fiber membranes so as to extend out beyond the end of the bundle of the hollow fiber membranes.
When the above-mentioned structure according to the present invention is employed, each hollow fiber membrane can be vibrated with maximum amplitude in a permissible range because no cylindrical casing covering the whole hollow fiber membranes is present at the periphery of the hollow fiber membrane cartridge. As a result, suspended materials accumulated on the outer surfaces of the hollow fiber membranes become easy to peel off at the time of washing by air bubbling, and the suspended materials peeled off become easy to discharge from the hollow fiber membrane cartridge. Therefore, the filtering capability can be maintained stably for a long period of time.
In addition, when the end of the bottom ring of the hollow fiber membrane cartridge is fixed by adhesion so as to extend out beyond the end of the bundle of the hollow fiber membranes, gas for air bubbling can be reserved inside the bottom ring and hence can be efficiently conducted to the hollow fiber membranes through the through-holes provided in the adhesion and fixation layer on the bottom ring side, so that washing by air bubbling can be satisfactorily carried out.
Furthermore, the present invention relates to a tank type or rack type filtration apparatus using the above-mentioned hollow fiber membrane cartridge(s).